Chapter 18 Functions of Metal Oxide for Thermoelectric Materials and Electronic Structures.

Abstract: We investigate metal oxides as thermoelectric (TE) materials and further as an additive for a certain purpose, i.e. from the view point of both theory, electronic structures, and experiment. The materials are ZnAlO, Fe₂O₃, and Sr₂FeMoO₆ (double perovskite). The oxides, Er₂O₃ and TiO₂ are the additives to ZnAlO and Fe₂O₃, respectively. ZnO has a large electrical resistivity, but the Al impurity level lies in an energy gap and becomes more semiconductive. We expect to reduce thermal conductivity by adding TiO₂ to Fe₂O₃. Lower electrical resistivity of 4×10⁻⁵ Ωm was obtained by Er-addition to ZnAlO. TiO₂ addition to Fe₂O₃ reduced thermal conductivity by 4Wm⁻¹ K⁻¹ which was a half as compared with non-additive. Sr₂FeMoO₆ was also calculated to find electronic structures depending on the state of spin to show the energy gap of 2.57eV for spin-up and metallic structure for spin-down. Experimentally, electrical resistivity of 2×10⁻⁴ Ωm was maintained up to 600K, then increased like a metal. This material has a very small Seebeck coefficient less than 20μVK⁻¹ which is not good for TE materials. [Copyright &y& Elsevier]